Lobachevski N. Geometrical Researches on the Theory of Parallels

Translated by G.B. Halsted. — La Salle: Illinois Open Court Publishing Company, 1914. — 64 p.Lobachevski was the first man ever to publish a non-Euclidean geometry.
Of the immortal essay now first appearing in English Gauss said, "The author has treated the matter with a master-hand and in the true geometer's spirit. I think I ought to call your attention to this book, whose perusal can not fail to give you the most vivid pleasure."